In a typical head, an inductive write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being located between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing bits of magnetic field information in tracks on moving media, such as in circular tracks on a rotating magnetic disk or longitudinal tracks on a moving magnetic tape.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium. Since magnetic flux decays as it travels down the length of the narrow second pole tip, shortening the second pole tip will increase the flux reaching the recording media. Therefore, performance can be optimized by aggressively placing the flare point close to the ABS.
FIG. 1 illustrates, schematically, a conventional recording medium such as used with conventional magnetic disc recording systems. This medium is utilized for recording magnetic impulses in or parallel to the plane of the medium itself. The recording medium, a recording disc in this instance, comprises basically a supporting substrate 100 of a suitable non-magnetic material such as glass, with an overlying coating 102 of a suitable and conventional magnetic layer.
FIG. 2 shows the operative relationship between a conventional recording/playback head 104, which may preferably be a thin film head, and a conventional recording medium, such as that of FIG. 1.
FIG. 3 illustrates schematically the orientation of magnetic impulses substantially perpendicular to the surface of the recording medium. For such perpendicular recording the medium includes an under layer 302 of a material having a high magnetic permeability. This under layer 302 is then provided with an overlying coating 304 of magnetic material preferably having a high coercivity relative to the under layer 302, such as a Co-containing material.
Two embodiments of storage systems with perpendicular heads 300 are illustrated in FIGS. 4 and 5 (not drawn to scale). The recording medium illustrated in FIG. 4 includes both the high permeability under layer 302 and the overlying coating 304 of magnetic material described with respect to FIG. 3 above. However, both of these layers 302′ and 304 are shown applied to a suitable substrate 306.
By this structure the magnetic lines of flux extending between the poles of the recording head loop into and out of the outer surface of the recording medium coating with the high permeability under layer of the recording medium causing the lines of flux to pass through the coating in a direction generally perpendicular to the surface of the medium to record information in the magnetically hard coating of the medium in the form of magnetic impulses having their axes of magnetization substantially perpendicular to the surface of the medium. The flux is channeled by the soft underlying coating 302 back to the return layer (P1) of the head 300.
FIG. 5 illustrates a similar structure in which the substrate 306 carries the layers 302 and 304 on each of its two opposed sides, with suitable recording heads 300 positioned adjacent the outer surface of the magnetic coating 304 on each side of the medium.
Fabrication of current-art perpendicular recording media (PMR) employs a Ru hcp-underlayer (where “hcp” refers to hexagonal closed packed) to control the c-axis orientation of a typically Co-based alloy magnetic recording layer. The hcp-underlayer structural characteristics play a key role in determining the crystalline order (texture), the grain size, and the defect density of the Co-based recording alloy. Furthermore, said underlayers also influence the formation of the desired granular structure comprising small Co-alloy grains segregated by a non-magnetic phase. Current underlayers for perpendicular recording do not meet all of the desired requirements for developing an optimum microstructure of the Co-based recording alloys.
FIG. 6 shows a current-art perpendicular media architecture 600. An adhesion layer 602 of an alloy of AlTi is deposited on a glass substrate 604. An antiferromagnetically coupled (AFC) structure 606 consisting primarily of CoTaZr is grown on the adhesion layer 602. This amorphous AFC soft ferromagnetic layer, known as the Soft UnderLayer (SUL), provides the flux closure path emanating from the perpendicular recording head flying above the topmost layer of the multilayer structure. (See FIGS. 4-5.) A NiFe thin layer 612 is employed to seed the correct growth orientation of an hcp-Ru metal bilayer structure 608 in order to align the c-axis of the Co-based alloy 610 out-of-the plane of the thin film.
Referring to FIG. 7, for perpendicular orientation of the magnetic axis, both the Ru and the Co-alloy (CoPtCr-Oxide) must grow with their basal planes [0001] 700 parallel to the thin film plane 702 and therefore their [11-20] crystal plane 704 is perpendicular to the thin film plane. Ru grows preferentially with such an orientation on NiFe. The texture tends to be poor and improvements in growth orientation of the Ru layer are attained by growing it under sputter conditions of low pressure and slow growth rates. Rocking Curve measurements support this experimental observation. However, low pressure and slow growth rates promote lateral grain growth which is undesirable for developing a recording layer microstructure comprising small, segregated magnetic grains with high coercivity. To reduce the recording layer grain size and achieve high coercivity and thus, high magnetic recording performance, the growth of the Ru underlayer is performed in two stages: first a ˜5 nm thick layer is grown employing a sputter pressure of ˜6 mTorr and a growth rate of ˜1 nm/s; next a 12 nm layer of Ru is deposited employing a sputter pressure of 55 mTorr and a growth rate of ˜2.5 nm/s.
The grain size reduction and the interface roughness achieved by the high pressure deposition of the Ru layer is critical and thus, acceptable recording characteristics can be derived even in the absence of the low pressure Ru sublayer in spite of the concomitant loss in growth orientation. The high pressure Ru layer is >10 nm to achieve the coercivity and nucleation field values for high recording performance. Increasing the thickness of the Ru layer too much is also undesirable, as it increases the physical distance between the SUL and the recording head. In addition when the Ru layer is too thick, it leads to the growth of crystallites with unfavorable growth orientations for rendering the magnetic axis out of plane. As will become apparent by reading the present disclosure, the thickness of the high pressure Ru in current-art perpendicular media is large enough to promote such undesirable Co-alloy growth orientation and thus there is a need to improve the degree of crystallographic texturing for both the Ru and Co-alloy layers.